This project will analyze the lethal and kinetic effects of new antitumor agents on various established human cell lines as a function of drug concentration, exposure time, and position of the cells in the cycle at the time of drug administration (cell cycle stage-dependent function). Cell kill will be assessed by the reduction in colony-forming capacity. Effects on cycle progression will be defined by sequential DNA histograms obtained by pulse cytophotometry. Combination chemotherapy using drug pairs on synchronized cells will be conducted to define the mechanisms of cell killing potentiation. Paired treatment will be conducted in simultaneous or staggered fashion. Other experiments will analyze the effect of sequential treatment of asynchronous cells with antitumor drugs. The first drug will be used as a synchronizing agent while the second drug will be used as a cytotoxic agent. These investigations on drug effects at the cellular level should contribute a rationale guideline for developing superior clinical therapeutic protocols.